I don’t do swim training (going to the pool is a real hassle), but I do cycling, running and other stuff. So I use the triathlete profile and set ‘swimming hours = 0’ in the plan creation wizard.
Even if it’s just a visual thing, it would make the product look more ‘pro’.
I imagine that as far as the UI goes the on-boarding wizard could just ask ‘what sports do you do?’ as a checklist to determine what ‘profile’ to set the user up as.
After the on-boarding, the other sports could be enabled at any time like it currently allows. Instead of changing the athlete type between runner/cyclist/triathlete, it lets one choose ‘swim/bike/run’ using a checklist. Adding/removing another sport would trigger a plan re-generation like it currently does.
On the back-end it could still use ‘triathlete w/ 0 hours swimming’ as the profile but this would just be hidden from the user.
A UI change like this would allow creating a ‘duathlete’ models of either bike/run or swim/bike or swim/run to happen on the back-end without the user needing to change their athlete profile manually.
Something like:

